问题
I want to iterate over a vector using .iter_mut()
and .map()
:
fn calculate_distances(planes : &mut Vec<Aeroplane>, x: f64, y: f64) {
fn calculate_distance(x1: &f64, y1: &f64, x2: &f64, y2: &f64) -> f6 { ... }
planes.iter_mut().map(|a| if a.position.is_some() {
let pos: &Position = &a.position.unwrap();
a.distance = Some(calculate_distance(&x, &y, &pos.latitude, &pos.longitude));
});
}
Aeroplane
contains instance of my Position
struct:
struct Position {
latitude: f64,
longitude: f64,
}
In my understanding I'm just borrowing the position information not moving out anything, but the borrow-checker refuses my code:
error[E0507]: cannot move out of borrowed content
--> src/main.rs:145:31
|
4 | let pos: &Position = &a.position.unwrap();
| ^ cannot move out of borrowed content
Where is my mistake?
回答1:
You are looking for Option::as_ref:
Converts from
Option<T>
toOption<&T>
.
The following code solves your problem:
let pos = a.position.as_ref().unwrap();
For a mutable version, Option::as_mut is provided.
Your code does not work, because as stated by turbulencetoo you try to move the data out of the Option
and borrow the moved data.
However, in this case the better solution would be if let:
if let Some(ref pos) = a.position {
a.distance = Some(calculate_distance(&x, &y, &pos.latitude, &pos.longitude));
}
See also:
- How do I borrow a reference to what is inside an Option<T>?
- How to unwrap a &Result<_,_>?
来源:https://stackoverflow.com/questions/51385381/how-to-borrow-an-unwrapped-optiont